In one type of plasma arc torch such as disclosed in U.S. Pat. Nos. 4,716,269; 4,581,516; and 4,580,032, an electrode is mounted in a torch head and includes a discharge end extending forwardly through and beyond an outlet of the torch head. A nozzle is positioned in surrounding spaced relation to at least the discharge end of the electrode. A first gas is supplied to the electrode and is ionized thereby to form a plasma. The plasma is discharged outwardly through an axial bore forming the discharge port of the nozzle. A second gas flows in surrounding engagement with the nozzle and provides not only cooling to the torch and work piece but a protective envelope for the plasma. During operation, a cooler work piece and torch can result in higher quality welds, cuts, and gouges.
It is believed that most prior art nozzles have a shortened cylindrical or conical shape with a taper converging toward the orifice of the nozzle. It has been determined that during operation of this type of torch, the desired amount of heat transfer from the nozzle to the cooling-stream has not occurred. This can result in overheating of the torch with a poor cut or weld quality. Additionally, the configuration of these prior art nozzles typically makes it difficult for an operator to guide the torch nozzle along a straight edge during cutting and allow the operator to cut in deep, narrow work areas.
It is therefore an object of this invention to provide a nozzle for a plasma arc torch which overcomes the aforementioned deficiencies of the prior art.
It is another object of this invention to provide a plasma arc torch of the type having a gas flow in surrounding engagement to the outer surface of the nozzle wherein the outer surface of the nozzle is configured so as to provide a surface on which the gas being discharged therealong can remain in close contact to provide an efficient heat transfer from the nozzle to the surrounding gas stream.